In general, industrial luminaires which are designed to be used indoors are arranged with appropriate hardware to hang the luminaire from a hook or rod, commonly near a ceiling. This is ordinary practice with luminaires using high intensity discharge lamps such as mercury vapor, metal halide and high pressure sodium. Such lamps have a ballast, such as a transformer, to step the available line voltage up to a level which is sufficient to properly energize the lamp. Most applications for such devices also require a current power factor correction device which can include a capacitor, and other components are also used, such as a starter or ignitor. A wide variety of circuit arrangements are available, and the various components which are used vary in size from one manufacturer to another. Additionally, the ballasts and capacitors differ in weight in accordance with different lamp wattages and lamp types.
These components, however, need to be fitted into a common housing commonly made out of die cast aluminum, fabricated sheet metal or extruded metal. Beneath the housing is a lamp holder to accept the lamp. To fully utilize the light emitted by the lamp, a formed or spun reflector is attached below the housing and above and around the lamp to reflect the light with directional control.
Unfortunately, because of the variety of different components having different weights, such luminaires tend to be unbalanced when they are suspended such that when the luminaire is placed in a horizontal position the center of gravity is laterally offset to a significant extent from the connection location which is a part of the housing and which, commonly, also provides a passageway for wires to enter the housing from the power source. Thus, when the luminaire is suspended, the housing swings until the center of gravity reaches a point directly below the point of suspension. This situation becomes a problem in the actual application because it projects the beam of light away from vertical or away from some other desired direction. Thus, it creates an uncontrolled beam distribution in addition to the fact that the tilting hanging luminaires are visually unacceptable.
This general problem has been recognized and various approaches have been taken to overcome the problem but with results which are not fully acceptable. One technique involves stacking all of the component parts such that their centers of gravity coincide essentially along one axis. While this technique works, it has the disadvantage of making the overall height of the luminaire considerably greater. Others use a dead weight the only function of which is to counterbalance, thus requiring various weights to match different sizes of ballast. Another luminaire is equipped with a fitting structure held with a plurality of bolts on a slotted track so that one can adjust the distance of the support with relation to the center of gravity to compensate for the weight unbalance. Other installations use simply a piece of string or wire to pull the fixture to its plumbed position, also a visually unacceptable solution.
Examples of prior art structures are found in the following U.S. patents.
U.S. Pat. No. 2,347,113 to King; PA0 U.S. Pat. No. 3,551,667 to Husby; PA0 U.S. Pat. No. 3,643,088 to Osteen et al.; PA0 U.S. Pat. No. 4,186,433 to Baldwin; PA0 U.S. Pat. No. 4,286,313 to Quioque.